Illumination is a technology particularly important to human beings. Starting with the use of lamps (light-emitting bodies) using trees or grease, many light-emitting body technologies have been developed until today. Today's wide-ranging light-emitting technologies have allowed implementation of, for example, incandescent lamps, fluorescent lamps, mercury lamps, and sodium lamps that are mainly used for general illumination; neon tubes frequently used for various displays; plasma displays; various laser light-emitting bodies; and light-emitting diodes.
In the light-emitting body technologies, both new and old, the following two main points are always required for a light-emitting body: (1) the energy required for light emission is as low as possible, in other words, the light-emitting body has a low-excitation characteristic, and (2) the brightness with respect to a certain excitation energy is as high as possible. With the advance of the light-emitting body technologies, the excitation energy has been reduced and the brightness has been increased. In reality, however, further reduction in excitation energy and increase in brightness are demanded. These are also urgent demands in consideration of, for example, the recent adverse effects on the environment caused by the use of fossil energy and the problem of exhaustion of fossil fuels in the near future.
In response to the demands for improving a low-excitation characteristic and increasing brightness, various efforts have conventionally been done. For example, as an example of efforts to improve the low-excitation characteristic, a technology is suggested using a nanocrystal fluorescent substance in order to improve a light-emitting efficiency of a fluorescent substance (Patent Document 1). This nanocrystal fluorescent substance is obtained by, for example, reacting manganese acetate and zinc acetate with sodium sulfide in a solvent. In this case, a zinc-sulfide nanocrystal fluorescent substance doped with manganese is obtained.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2000-104058